This invention concerns generally the automatic control of vertical adjustment of a harvester header and, in particular, control so as to maintain a selected attitude in a floating forward mounted gatherer portion such as a belt pickup.
It is already known to provide automatic attitude control for a belt pickup, see for example, U.S. Pat. No. 4,171,606 Ziegler et al, also assigned to the assignee of the present invention. For efficient operation, the forward end of the belt pickup must follow the ground quite closely and conventional machines are fitted with a pair of wide-spaced gauge wheels running just ahead and outside of the forward portion of the belt. The pickup is free to pivot relative to the header about a transverse axis and also it is torsionally flexible so that the opposite ends can float independently. Normally, the belt rollers of the pickup are stiff enough that there is negligible beam deflection along the length of the pickup.
It is known to provide individual attitude sensors, one for each end of the pickup. These sensors sense deviations from an operator selected set point of the angle between the floating pickup and an auger platform portion of the header. The requirements for good function without damage to the pickup are that a signal from either end must be sufficient to raise the header whereas signals from both ends are required before the header is lowered (to ensure that, in uneven ground conditions, one end of the header is not run into the ground). However, when a pair of electrical sensors are used, the circuitry must include series connections of the sensors in the "lower" circuit and parallel connection of the sensors or their switches in the "raise" circuit. Duplication of electrical sensors and provision of the required circuitry becomes relatively expensive and the greater complication of the system makes it inherently less reliable.